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The MG 42 (shortened from German Maschinengewehr 1942, meaning "Machine Gun 1942") was a general purpose machine gun that was developed for and entered service with the German Wehrmacht in 1942 during World War II. The 7.92mmriflecaliber weapon was developed from, and was intended to supplant the MG 34, though both would continue to be used and manufactured until the end of that war.

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The MG 42 has the highest average rate of fire of any single-barreledlight machine gun, resulting in a distinct muzzle report. It has a proven record of reliability, durability, simplicity, and ease of operator use. The MG 42's lineage continued past Germany's defeat, forming the basis for the nearly identical MG 1, and subsequently improved into the still very similar MG 2, which was in turn followed by the MG 3. It also spawned the Swiss MG 710 and the MG 42/59. It and the MG 3 were in service with many armies during the Cold War and remain so into the 21st century.

Development of the MG 42 was by Metall und Lackierwarenfabrik Johannes Großfuß AG and resulted from further attempts at improving on the MG 34, particularly making them easier to mass-manufacture. The internals were still a short recoil system like the MG 34, but the bolt locking system was a design originally patented by Edward Stecke of Poland.

A limited run of about 1,500 of its immediate predecessor, the MG 34/41, had been completed in 1941 and tested in combat trials. It was officially accepted, and the main manufacturing of the production design began in 1942; contracts going to Großfuß, Mauser-Werke, Gustloff-Werke, and others. Production during the war amounted to over 400,000 (17,915 units in 1942, 116,725 in 1943, 211,806 in 1944, and 61,877 in 1945). It could be produced in roughly half the number of man-hours of the MG 34, using less metal in the process.

One of the weapon's most noted features was its comparatively high cyclic rate of about 1,200 rounds per minute, with some versions that are up to 1,800 rounds per minute; much faster than the British Vickers machine gun at 600 round/min, though it must be noted that the Vickers had superior range, power, and accuracy being a heavy machine gun.

At such a high rate, the human ear cannot easily discern the sound of individual bullets being fired, and in use the gun makes a sound described as like "ripping a piece of cloth" and giving rise to the nickname "Hitler's buzzsaw", or, more coarsely, "Hitler's zipper" (Soviet soldiers called it the "linoleum ripper"). German soldiers called it Hitlersäge ("Hitler's saw") or "Bonesaw". The gun was sometimes called the "Spandau" by British troops from the manufacturer's plates noting the district of Berlin where some of the weapons were produced. It was also known among British troops as the "Calico-tearer" due to its distinctive sound.

So distinct and terrifying was the weapon, that the United States Army created training films to aid its soldiers in dealing with the psychological trauma of facing the weapon in battle. The high rate of fire had resulted from experiments with preceding weapons that concluded that since a soldier only has a short window of time to shoot at an enemy, it was imperative to fire the highest number of bullets possible to increase the likelihood of a hit. (This principle was also behind the Vickers GO aircraft gun.) The disadvantage of this principle is that the weapon consumed exorbitant amounts of ammunition and quickly overheated its barrel, making sustained fire problematic.

In the late 1930s, the MG 34 had proved satisfactory. However, it did have its drawbacks, such as sensitivity to dust and comparatively expensive production. One attempt at improvement was the MG 34S, an incremental improvement on the basic 34 design. A much bigger improvement would come from a design firm, Metall-und-Lackierwarenfabrik Johannes Großfuß AG, experts in pressed and punched steel parts. Their efforts resulted in a dramatic reduction in complexity — it took 75 man-hours to complete the new gun as opposed to 150 man-hours for the MG 34, and cost 250 German reichsmark RM as opposed to 327 RM.

The resulting MG 39 (redesignated MG 42 when adopted in 1942) remained largely similar to the earlier MG 34, a deliberate decision made in order to maintain familiarity. The only major change from the gunner's perspective was dropping the drum-feed options, leaving it with a loose belt of ammunition only, and to further increase the rate of fire. Although made of relatively cheap parts, the prototypes also proved to be considerably more rugged and resistant to jamming than the somewhat "temperamental" MG 34.

The MG 42 weighed 11.6kg in the "light" role with the bipod, lighter than the MG 34 and easily portable. The bipod, the same one used on the MG 34, could be mounted to the front or the center of the gun depending on where it was being used. For sustained fire use, it was matched to the newly-developed Lafette 42tripod, which weighed 20.5kg on its own. The barrel was lighter than the MG 34's and heated more quickly, but could be replaced in seconds by an experienced gunner.

The operating crew of an MG 42 consisted of three men: the gunner, the ammunition loader (also barrel carrier), and the spotter. The gunner of the weapon was preferably a junior non-commissioned officer (or Unteroffizier). It was possible for operating crews to lay down a non-stop barrage of fire, ceasing only when the barrel had to be replaced. This allowed the three-man crew of an MG 42 to tie up significantly larger numbers of enemy troops. Both the Americans and the British trained their troops to take cover from the fire of an MG 42, and assault the position during the small window of barrel replacement. The high rate of fire of the MG 42 sometimes proved a liability — mainly in that, while the weapon could be used to devastating effect, it could quickly exhaust its ammunition supply. For this reason, it was not uncommon for all soldiers operating near an MG 42 to carry extra ammunition, thus providing the MG 42 with a backup source when its main supply was exhausted.

The MG 42 is air-cooled, open bolt, recoil-operated, with a short recoiling barrel, light machine gun. It fires in the full automatic mode only. The operation functions as follows:

The trigger is pulled and this releases the bolt assembly.

The bolt assembly is pushed forward by the mainspring; the feed lug on the bolt head strips a round from the belt link and feeds into the chamber.

As the round is chambered, the bolt rollers, positioned in slots on the bolt head, are allowed by the receiver tracks to move outwards under the influence of the wedge/bolt body into matching slots in the barrel extension and lock the bolt in place against the breech.

As the bolt locks are fully engaged, the wedge contacts the rear of the firing pin and drives it into the primer initiating the firing sequence.

As the bullet passes down the barrel, the recoil drives the barrel and the bolt assembly rearward, there is a recoil booster fitted to the muzzle to increase the recoil velocity of the barrel and the bolt during the short recoil action.

As the bolt assembly moves rearward, the stationary receiver tracks pinch the locking rollers inward, accelerating the wedge and bolt body, as well as unlocking the bolt head from the barrel extension.

The rearward motion of the barrel is arrested by the barrel spring.

The spent cartridge is held by the extractor to the bolt head until the ejector bar in the rear of the bolt contacts the buffer and this ejects the empty case from the weapon.

The momentum of the bolt assembly compresses the buffer spring and the bolt assembly rebounds off the buffer with sufficient energy to strip, fed and fire the next round.

The sequence continues until the trigger is released. The mainspring is only needed to chamber and fire the first round.

Due to the extremely high rate of fire the trigger is designed to eliminate the possibility of slowly releasing the trigger and having the bolt assembly slam into a partially raised sear. The high energy of the reciprocating mass would severely damage the sear in this case, possibly rendering the sear incapable of stopping the bolt resulting in a run-a-way gun.

When the trigger is pulled back, the rear tab on the trigger pushes up on the front of the sear rotating it so the nose drops, at the same time the front of the trigger draws the lifter down. When the sear nose is sufficiently low to release the bolt the lifter has passed below the front of the sear. When the trigger is released, the back of the trigger drops but the front, with the lifter, rises and the lifter catches the front of the sear and holds in down. As the trigger continues being released the lifter is pushed upwards until the top of the lifter is in the bolt path. The bolt then strikes the lifter; it pivots about its pin in the trigger and releases the front of the sear. The sear under action of its spring snaps up and catches the bolt with the entire engaging surface.

The shoulder stock (or butt) is designed to permit gripping with the left hand to hold it secure against the shoulder. The considerable recoil can cause the stock to creep from its intended position if the weapon is not properly "seated" in the shoulder.

In 1944, the acute material shortages of the Third Reich led to a newer version, the MG 45 (or MG 42V), which had a different operation mechanism and used retarded blowback as opposed to roller locking, used steel of lesser quality, reduced weight to only 9kg, retaining the horizontal cocking handle. First tests were undertaken in June 1944, but development dragged on and eventually only ten were ever built. The tested MG 45/42V fired 120,000 rounds in succession at a rate of fire around 1,350 rounds per minute.

The MG 42V had some influence in the post-war development of roller-delayed blowback system, as employed in Heckler & Koch modern small arms. The MG 45/MG 42V should be considered a different firearm however as the mechanisms of these guns were different from that of the MG 42.

The American military tried to copy the MG 42 during the war, the new version being adapted for the .30-06 cartridge. Saginaw Steering Gear constructed a working prototype designated as the T24 machine gun. However, a design flaw in the prototype and the realization that the cartridge might be too powerful for the gun's mechanism to easily cope with resulted in the discarding of the project. However, its belt-feeding mechanism was adopted for the design of the M60.

The MG 42, with small modifications, resulted in the MG 42/59 and Rheinmetall MG3, which is the primary general-purpose machine gun of the modern German armed forces (Bundeswehr). A number of other armies around the world have adopted versions of the original, especially the MG 3, and it remains in widespread service today. The U.S. Army's M60 uses a modified belt-feed mechanism from the MG 42 (developed from the 34). The T161 beat the FG 42 derived T52 during tests in the 1950s to become the M60. The T161 used a different gas system and was easier to manufacture than the T52, but they both used a similar belt-feed and basic configuration.

Rate of fire: Variable, from 1,100 round/min to 1,600 round/min or more depending on installed bolt weight (different weight bolt components introduced to regulate rate of fire, lighter assemblies providing faster rates of fire). Throat erosion and component wear also introduced significant variation. Up to 1,800 round/min on the MG 45 or without "recoil booster" (Rückstoßverstärker).

Parts changes:

Barrel: 3 to 7 seconds

Barrel and lock: 25 to 30 seconds

The MG 42 was adopted by a number of armed organizations after the war, and was copied or license-built as well. There is also a Yugoslav version of the MG 42 known as the Zastava M53, which retains the 7.92×57mm caliber.